DEVELOPMENT OF MAESUPIUM 77 



stage during the whole time of the pouch 

 development, and have nothing to do with its 

 formation, as Klaatsch presumed. 



As regards the development of the pouch 

 in the other families of the Marsupialia, it 

 need only be mentioned that in the Dasyuridte, 

 as in the Didelphyidse, the pouch is formed at 

 the expense of a number of marsupial pockets, 

 and that in the remaining families also its 

 development is always connected with their 

 appearance. Accordingly, it may be concluded 

 that the marsupial pockets in general represent 

 the starting-point of the pouch development, 

 even though in the higher marsupial families 

 modifications have taken place, adapted to 

 bring about a fiu-ther enlargement of the 

 simple marsupium originally derived from the 

 marsupial pockets alone. Fig. 29, Fig. 30a, 

 and Fig. 30b demonstrate the presence of the 

 marsupial pockets in Trichosurus, and it is of 

 interest to notice that in this and other genera 

 they do not appear only as folds, but also as 

 solid epidermal ingrowths, which later become 

 hollowed out. 



An extremely important conclusion follows 

 from our observations — that is, that the 



